If you decide to try your hand at breeding the brotogeris, keep several things in mind. First is the availability of stock. Ideal would be bonded pairs. However, if that's not possible then single birds will work fine. You just need to work with them. If you have several you could put them in an open flight and let them select their mate. This is a good idea providing that they all have equal physical strength, and you monitor them constantly. As soon as you see pairs together, pull them from the flight. Make sure they are in fact a male and female. They should be housed in large individual cages that are not stacked. The cage location should be where there is some privacy from human traffic. They will breed better if kept a distance from large parrots.
The nest box I use is called an English budgie box. It measures 10"w x 10"h x 7"d. I prefer aspen shavings over pine as it seems less dusty.
NOTE: In 2010 I had custom nest boxes made. They measure 10"w x 13.5"h x 7.5"d. 2010 was the best breeding season since I started this project in 1999.
2011 was the second best breeding season I've had. I believe the new nest boxes played a major role in the Grey-cheeked breeding success.